This invention relates to integrated circuits, and more particularly, to nonvolatile memory element circuitry for integrated circuits.
Integrated circuits sometimes contain volatile memory elements. For example, dynamic random-access memory (DRAM) and static random-access memory (SRAM) memory chips include numerous rows and columns of volatile memory cells. Devices such as application-specific integrated circuits, microprocessors, and programmable logic device integrated circuits also may contain volatile memory.
Nonvolatile memory is used for persistent data storage. For example, nonvolatile memory is sometimes used for storing image files in a camera or for storing documents on a universal serial bus memory key.
Nonvolatile memory based on fuses and antifuses also is sometimes used in integrated circuits. Unlike the reusable nonvolatile memory that is typically installed in cameras and other electronic devices, nonvolatile memory based on fuses and antifuses need not be reprogrammable. Rather, one-time use scenarios are acceptable. Examples of situations in which one-time programmable nonvolatile memory elements such as one-time programmable fuses and antifuses may be used include situations in which a unique identification code is loaded onto an integrated circuit or in which repair settings are permanently loaded into an integrated circuit as part of a manufacturing process. Repair settings might, for example, permanently switch redundant circuitry into use in place of defective circuitry, thereby effectuating a permanent repair of the integrated circuit before shipping to an end user.
When forming nonvolatile memory elements for applications such as redundancy schemes and permanent data storage, it is desirable to select a memory element technology that exhibits satisfactory levels of permanency and power consumption. Tradition nonvolatile memory elements are sometimes formed using laser-programmed links or electrically programmed polysilicon fuses. Laser programming of nonvolatile memory elements requires special programming tools that can add undesirable cost and complexity to the manufacturing process. Polysilicon fuses can be satisfactory, but are only available on integrated circuits that contain polysilicon structures. In some modern semiconductor fabrication processes, polysilicon gate layers are being replaced with metal gate layers. Although additional process steps could be included in this type of fabrication process to form polysilicon memory element structures, the inclusion of additional process steps tends to drive up manufacturing costs and makes manufacturing more difficult.
It would therefore be desirable to be able to provide improved nonvolatile memory element circuitry for integrated circuits.